Use case

I noticed this @chunhtai's comment at #173418 (comment):

"we should check defaultTargetPlatform instead of from the theme, if for some reason someone wants android feels and look on an iOS, the voice over will still be broken"

Indeed, in case users explicitly configure a specific platform (let's give it as Android for eg), but run on another platforms (let's give it as iOS for eg), accessibility might work incorrectly.
There are a few existing widgets that use platform from the theme to check:

1. ExpansionTile:

2. AppBar:

3. Dialog:

Proposal

Use defaultTargetPlatform instead of using platform from the theme.